1. Field of the Invention
The present invention relates to a method of preparing a coalesced spandex. More particularly, it relates to a method for dry-spinning a solution of a high-melting thermoplastic polyurethane, bundling the resulting spandex, and fusing the resulting bundle to form the coalesced multifilament spandex by a method which does not employ false-twisting.
2. Description of the Background Art
In the conventional production of a coalesced spandex by dry spinning, a solution of polyurethane or polyurethaneurea is prepared and extruded through spinneret holes into a spinning column. Heat is applied to the inside of the column to drive off the solvent and form filaments. Such filaments are customarily quite small in diameter in order to permit rapid evaporation of solvent. In order to make filaments with larger diameters and to improve the uniformity of the final product, a plurality of filaments are normally bundled together and cohered to each other (xe2x80x9ccoalescedxe2x80x9d) along their lengths by passing them through a jet such as described in U.S. Pat. No. 3,353,344. Such a false twist coalescence method is described in, for example, U.S. Pat. No. 3,094,374. Due to the random distribution of any nonuniformities along the length of individual filaments, such irregularities are effectively cancelled out when a number of filaments are thus coalesced, and the resulting coalesced multifilament spandex has improved uniformity over the individual filaments.
European published Patent Application Number 756026 discloses a method wherein immediately after dry-spinning of segmented polyurethaneureas which are not thermoplastic, the filaments are slightly bonded by passing them through a xe2x80x9cthread control element with comb-like shapexe2x80x9d immediately after spinning to form a multifilament which can be readily and easily split into single filaments.
Japanese published Patent Application Number 53-139847 describes melt-spinning of a low-melting polyurethane from widely spaced spinneret holes and the bonding of the resulting filaments into a coalesced multifilament spandex by passing them through a guide placed at a selected distance from the face of the spinneret.
Spandex is widely used in various applications such as apparel because it has desirable characteristics including high stretch and recovery. Expanding applications have led to new needs such as high uniformity combined with mechanical properties that are available from, for example, thermoplastic polyurethanes and polyurethaneureas. Spandex with desirable properties such as good heat settability, high elastic recovery, and good resistance to environmental conditions can be the prepared by dry-spinning a high-melting thermoplastic polyurethane to make a spandex such as that disclosed in International Patent Application Number WO95/23883. Good heat settability is an advantage, for example, when the spandex is to be used in combination with other fibers such as wool which should not be exposed to the temperatures necessary to heat-set such spandex.
However, spandex uniformity tends to be unsatisfactorily low when filaments of such a polyurethane are dry-spun and coalesced by the conventional false-twist coalescence method, perhaps due to fluctuations in the twisting force. As a result, the combination of good uniformity with the desirable properties of a dry-spun thermoplastic polyurethane is still needed.
In the method of the present invention a solution of high-melting thermoplastic polyurethane is extruded from a spinneret into a heated atmosphere to produce a plurality of filaments which are then brought into a side-by-side relationship with each other and fused into a coalesced multifilament by passing the filaments over or through a guide by a method which does not employ false-twisting.
As used herein xe2x80x9cspandexxe2x80x9d has its usual meaning, that is, a manufactured fiber in which the fiber-forming substance is a long chain synthetic elastomer comprised of at least 85% by weight of a segmented polyurethane. xe2x80x9cThermoplastic polyurethanexe2x80x9d and xe2x80x9cthermoplastic polyurethaneureaxe2x80x9d mean a polyurethane and a polyurethaneurea, respectively, with a melting point (xe2x80x9cTmxe2x80x9d) in the range of 150-270xc2x0 C., preferably in the range of 160xc2x0 C. to 250xc2x0 C. and most preferably in the range of 230xc2x0 C. to 250xc2x0 C. when measured by differential scanning calorimetry (hereinafter xe2x80x9cDSCxe2x80x9d) and a DSC-measured glass transition temperature (xe2x80x9cTgxe2x80x9d) of no more than 0xc2x0 C., preferably no more than xe2x88x9220xc2x0 C.
The present invention provides a method for preparing a coalesced multifilament spandex comprising:
dry spinning a thermoplastic polyurethane to form as-spun filaments;
bundling a plurality of the as-spun filaments in a first guide;
passing the bundled filaments through a second guide to form a coalesced multifilament, neither the first guide nor the second guide creating false-twist in the filaments; and
winding up the coalesced multifilament;
wherein the thermoplastic polyurethane has a melting point in the range of about 230xc2x0 C. to 250xc2x0 C. and a glass-transition temperature no higher than about 0xc2x0 C. Preferably, the first guide is a comb-shaped guide and the second guide is a slit guide.
The method of the present invention can be applied to filaments comprising primarily polyurethanes, polyurethaneureas, or blends of polyurethanes and polyurethaneureas, so long as the polyurethane, polyurethaneurea or mixture thereof has a Tm in the range of about 150-270xc2x0 C., preferably in the range of about 160-250xc2x0 C., and most preferably in the range of about 230xc2x0 C. to 250xc2x0 C., and has a Tg of no more than about 0xc2x0 C., preferably no more than about xe2x88x9220xc2x0 C. Such high melting temperatures generally require even higher (and therefore impractical) processing temperatures for melt-spinning and, therefore, the resulting spandex is best prepared by dry-spinning from solution.
In order to combine good coalescence by the method of the present invention with good heat settability and satisfactory heat resistance in use, polyurethanes with melting points below 150xc2x0 C. or above 270xc2x0 C. should be avoided. If the melting point is too low, the heat resistance is insufficient. If the melting point is too high, the heat settability and fusability by the method of the present invention are insufficient.
Spandex can be prepared by reacting a polymeric glycol with a diisocyanate to form a xe2x80x9ccapped glycolxe2x80x9d, dissolving the capped glycol in a suitable solvent, reacting the dissolved capped glycol with a difunctional chain extender to form the polyurethane or polyurethaneurea in solution, and dry-spinning the solution through a heated spinning column. Suitable solvents include dimethylacetamide (DMAc), dimethyl-formamide, N-methylpyrrolidone, and the like. This xe2x80x9cprepolymer methodxe2x80x9d is preferred when the chain extender is a diamine. Alternatively, when the chain extender is a diol, melt polymerization can also be used. Reaction of all ingredients can also be carried out in solution for diamine- and diolextended polymers. When the chain extender is a diol, such polymers are polyurethanes, and when the chain extender is a diamine, such polymers are polyurethaneureas. In solution and melt polymerization, especially when the chain extender is a diol, the ingredients can be added sequentially or all at once (the xe2x80x9cone shot methodxe2x80x9d). In order to make the spandex according to the method of the present invention when the polymer is made in the melt, the polymer is dissolved in a suitable solvent by any suitable method prior to dry-spinning. The solution can also be prepared from one type of polyurethane or two or more types of polyurethane.
The polymeric glycol can be a polyether diol or a polyester diol. Suitable polyether diols include those derived from butanediol, 3-methyl-1,5-pentanediol, tetrahydrofuran, 3-methyltetrahydrofuran, and copolymers thereof. Preferred polyether dials include polytetramethyleneether glycol (PTMEG) and PTMEG having copolymerized therein minor amounts of 3-methyltetrahydrofuran. Glycol-terminated polyesters which can be used in conjunction with the present invention include the reaction products of ethylene glycol, butanediol, and 2,2-dimethyl-1,3-propane diol with diacids such as adipic acid, succinic is acid, and dodecanedioic acid. Copolymers can also be used.
Any organic diisocyanate can be used, for example bis(p-isocyanatophenyl)methane (xe2x80x9cMDIxe2x80x9d), tolylene diisocyanate, bis(4-isocyanatocyclohexyl)methane (xe2x80x9cHMDIxe2x80x9d), hexamethylene diisocyanate, and 3,3,5-trimethyl-5-methylene-cyclohexyl diisocyanate.
Dial chain extenders which can be used include ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,2-propanediol, 1,4-cyclohexanediol, 1,4-cyciohexane-dimethanol, 1,4bis(p-hydroxyethoxy)benzene, bis(xcex2-hydroxyethyl)tere-phthalate, and p-xylenediol. Ethylene glycol and 1,3-propanediol are preferred.
Examples of useful diamine chain extenders include ethylenediamine, 2-methyl-1,5-pentanediamine, 1,3-diamino-cyclohexane, 1,2-propanediamine, 1,3-diaminopropane, 1,4-diaminobutane, and 1,6-diaminohexane. Ethylenediamine is preferred.
A small amount of a monofunctional chain terminator such as diethylamine can be added with the chain extender to control molecular weight.
The diisocyanate and chain extender should be chosen together in order to maintain the Tm and Tg in the selected range. A diol chain extender is preferred when an aromatic diisocyanate such as MDI is used. An aliphatic diisocyanate such as HMDI is preferred when the chain extender is a diamine. More preferred combinations are MDI with ethylene glycol and HMDI with ethylenediamine.
Mixtures of diol and diamine chain extenders can be used, and polymer blends of polyurethanes and polyurethanureas are also acceptable, provided the Tm and Tg are in the specified ranges.
Various additives can be added by any suitable method to the polymer solution before spinning, provided the polymer is not adversely affected with regard to its performance under the conditions of the inventive process. Stabilizers to provide resistance to light and oxidation include 2,6di-t-butyl-4-methylphenol (butylated hydroxytoluene or BHT), hindered phenols such as Sumilizer GA-80 (made by Sumitomo Kagaku, Osaka, Japan), benzotriazole and derivatives thereof, phosphorus agents such as Sumilizer P-16 (also made by Sumitomo Kagaku), hindered amine light stabilizers, inorganic pigments such as titanium dioxide and carbon black, metal soaps such as magnesium stearate, bactericides such as silver, zinc, and compounds thereof, deodorizers, lubricants such as various types of silicone and mineral oil, mixtures of huntite and hydromagnesite, barium sulfate, cerium oxide, and various antistatic agents including phosphoric acids.
When especially high durability to light and nitrogen oxides is desired, it is effective to use a nitrogen oxide resisting agent such as HM-150 made by Japan Hydrazine (Tokyo, Japan), thermal oxidation stabilizers such as Sumilizer GA-80 made by Sumitomo Kagaku, and photostabilizers such as Sumisorb 300#622, also made by Sumitomo Kagaku.
The times and methods of adding these additives can vary. For example, they can be mixed into the polyurethane solution by a conventional method such as with a static mixer.
The polymer solution produced in this way is extruded from a spinneret into a heated atmosphere. The heated atmosphere is usually composed primarily of an inert gas such as nitrogen. However, the atmosphere can also contain water vapor and/or steam, as well as other gases. A vacuum can also be applied to the heated atmosphere.
The arrangement of holes in the spinneret can vary. Preferably, however, the spinneret holes are arranged in groups comprising two, three, four or more holes, and therefore each group can produce a plurality of individual filaments. The distance between the holes within each such group is preferably smaller than the distance between the nearest members of adjacent groups of holes.
The extruded solution is made into filaments by drying with heat in a spinning column. These filaments can be paralleled (bundled) by passing them through a first, comb-shaped guide which collects the filaments from each group of spinneret holes so that the filaments are later coalesced (fused) only with other filaments from their own group of spinneret holes. The bundled filaments can then be fused into a coalesced multifilament by passing them over a second guide. The comb guide can be located near the bottom of the spinning column, and the second guide, just outside the bottom of the spinning column, where false-twist jets would normally be in conventional dry-spinning of non-thermoplastic polyurethanes. In order to obtain well-coalesced, non-splittable multifilaments, it is preferred that lubricating agents such as silicone oil not be applied to the as-spun filament before it is thus bundled and coalesced. Contrary to the method ordinarily used in making coalesced multifilaments by dry-spinning, false twisting is not used in the present invention. It was highly unexpected that passing dry-spun filaments over a guide without false-twisting would result in a coalesced multifilament and that this process would give higher quality spandex than using a false-twist coalescence jet.
There are several types of fiber guides that can be used in the method of the present invention to coalesce the as-spun filaments. Examples include slit guides with V-shaped or U-shaped bottoms, rolls with V- or U-shaped grooves cut into them, closed-ring guides, and pigtail guides, which have the form of a short open-ended helix. Such guides can be ceramic (for example alumina-based) and can be used individually or in combination in the method of the present invention. It is not necessary to heat the guides in the present method.
After coalescence, the multifilament is wound up on a bobbin or tubecore to form a wound package.
The spandex of the present invention can be used alone or with various other types of fibers by knitting, weaving, or stitching it. For example, it can be used appropriately in underwear, stockings, pantyhose, circular knits, tricot knits, bathing suits, ski pants, socks, work clothes, fireproof clothing, western style clothes, men""s suits and women""s clothes when combined with wool, golf pants, wet suits, brassieres, girdles, gloves, socks, and other various types of control garments, in sanitary products such as disposable diapers, waterproof materials, safety clothing and laboratory wear, hairnets, for wrapping fruits and vegetables, foods, horticulture, electrical insulating materials, cloth wipes, copy cleaners, and gaskets.
The present invention is further explained in detail below in the Examples.